Description

A model was developed to predict site index (base age 50 years) for longleaf pine (Pinus palustris Mill.). The model, named PPSITE, was based on soil characteristics, site location on the landscape, and land history. The model was constrained so that the relationship between site index and each soil-site variable was consistent with what was known about the biology of the species. The model was quantified empirically with information available from the literature or other sources and with data collected for this study from 50 stands. Because of the way the model was developed, PPSITE is an example of an expert, or knowledge-based, system. For the original set of 50 stands, the difference between site index estimated from tree ages and heights and site index predicted by the model averaged 2.8 feet with the chi-square test of accuracy indicating that site index prediction should be within 5.5 feet (p<0.05). A second test of the model with reserved data from an additional 19 stands indicated that the model's predictions were within +4.5 feet (pP. tueda L.), this model indicates that maximum site index is less for longleaf pine and that longleaf pine is more sensitive to storm damage, more sensitive to conditions at stand establishment, less tolerant of very poor soil drainage, and less sensitive to suboptimum soil nutrition than loblolly pine. The PPSITE model is available as an interactive computer program for IBM-compatible personal computers. Supplemental information is provided in appendices to assist users in operating the program and in understanding the structure of the underlying model.